The invention relates to a method for tracing objects, to a system for tracing objects, to a tag for a system for tracing objects, to a transmitter station for a system for tracing objects and to a computer program for use in a system for tracing objects.
A method, a system, a tag, a transmitter station and a computer program for tracing objects are described in United States patent 6 057 756. According to this patent a set of receiver stations is used which receive reaction signals from the tags. The transmitters and receivers are coupled to a controller by a transmitter bus and a receiver bus. The controller is typically activated by a request for an item and causes an interrogation signal to be transmitted by at least one of the transmitters. Various tagged objects will be subjected to the interrogation signal, but only one objectxe2x80x94the one requested by the userxe2x80x94will respond to the interrogation signal. The interrogation signal triggers the tag matching the interrogation signal to send a responsive signal, which signal is detected by the nearest one of the receiver stations and the location of the object can then be reported.
European patent application 0 467 036 describes a system in which the transmitter and the receiver are combined in interrogator stations. It is described to determine the approximate location of tags by identifying the location of the interrogator, which has received the responsive signal from the tag.
Other examples in which the approximate location of tags is determined in accordance with the positions of receivers are described in international patent applications WO 98/16849, WO/99123623, WO 99/62039, WO 99/67737, WO 00/16564. A disadvantage of these known methods and systems is that each of the interrogators needs to communicate individually with the controller.
A similar disadvantage also applies to the system described in UK patent application 2 298 098 according to which a plurality of slave stations receive signals from a transponder and the position of the transponder is determined from the time delays with which signals from the transponder are received by the slave stations.
In European patent application 0 965 857 a system for determining the position of a tag, with particular accuracy in the area of an entrance is described. According to this document, an angular difference of preferably 180xc2x0 between the phases of the field of a cell in which the transponder is detected and of the fields of neighbouring overlapping cells is provided, so that the transponder can detect and signal to a receiver that it is in de area of the overlap and the direction in which the transponder is moving can be determined from the phase change occurring when passing from one field into the overlap and from the overlap into the other field. This allows detection of the position and direction of motion of a transponder in the area of for instance a gate at the exit of a building with an accuracy of a few centimetres, which, in turn, allows early and reliable warning that a transponder is brought outside the building. However, the transmitters need to be able to communicate individually with the control unit to be able to change the phase of the field generated thereby in response to detection of a transponder in a neighbouring field.
In UK patent application 2 353 910, an asset tracking system is described in which a beacon transmits a signal including an ID signal. An asset decodes the signal to determine the ID signal and sends the beacon ID to a central server. It is further described that this transmission may be over any communications network, for example a LAN or a telephone network, or a wireless network comprising a relay system through the beacons themselves. The server computes the physical location from the beacon ID, or the server detects a change of location of the asset determined from a list of beacons and a list of asset locations held by the server. Bluetooth digital radio technology is described as the preferred implementation. A problem of this system is that a network is required to communicate the signals from the asset to the central server.
It is an object of the invention to facilitate tracing of objects (which may also includes human persons or animals), in particular by providing a solution requiring relatively little installation effort.
According to the present invention, this object is achieved by providing a method for tracing objects, comprising:
providing a plurality of distributed transmitter stations, each of said transmitter stations transmitting an activation signal;
attaching a tag to each object to be monitored, each of said tags receiving the activation signal from one of said transmitter stations when in an operating area of said one of said transmitter stations, the received activation signal causing the tag to transmit a reaction signal and the operating areas of said transmitter stations being spatially distributed;
providing at least one receiver station, said receiver station receiving said reaction signals transmitted by said tags; and
registering data representing positions of tags in accordance with said reaction signals received by said at least one receiver station;
wherein the activation signal transmitted by each of said transmitter stations includes a predetermined transmitter station code associated to that transmitter station, the transmitter station codes transmitted by at least two of said transmitter stations being mutually different and distinguishing activation signals from at least one of said transmitter stations from activation signals from at least one other one of said transmitter stations;
said reaction signals transmitted by activated ones of said tags each including the transmitter station code included in the received activation signal that caused the tag to transmit said reaction signal; and
the registration of data representing positions of tags being carried out in accordance with different transmitter station codes received from said tags by said receiver station or each of said receiver stations.
The invention can also be embodied in a system specifically adapted for use in such a method, which system, includes:
a plurality of distributed transmitter stations for transmitting activation signals;
a plurality of tags for attachment to objects to be monitored, each of said tags including a receiver for receiving the activation signal from one of said transmitter stations when in the operating area of said one of said transmitter stations and a transmitter communicating with the receiver for activation of the transmitter to transmit a reaction signal in response to receipt of an activation signal by the receiver, the operating areas of said transmitter stations being spatially distributed;
at least one receiver station for receiving said reaction signals transmitted by said tags; and
a data registration structure communicating with said at least one receiver station for registering data representing positions of tags in accordance with said reaction signals received by said at least one receiver station;
wherein said transmitter stations are each adapted for including a predetermined transmitter station code in the activation signal, the transmitter station codes of at least two of said transmitter stations being mutually different and mutually distinguishing activation signals from at least one of said transmitter stations from activation signals from at least one other one of said transmitter stations;
said tags each being adapted for receiving transmitter station codes in the received activation signal and for including the transmitter station code of the activation signal that caused the reaction signal to be transmitted in the reaction signal transmitted by that tag; and
said data registration structure being adapted for registration of data representing different positions of activated ones of tags in accordance with different transmitter station codes received from said tags by said receiver station or each of said receiver stations.
The invention can also be embodied in a computer program, that may be provided in machine readable form as a signal or on a data carrier, for controlling a particular embodiment of the method according to the invention in which warning signals are selectively not generated in response to authorized combinations of codes received from the tags. According to the invention this object is achieved with a computer program including:
instructions for causing a data registration structure to read reaction signals inputted from a receiver station and to register data representing positions of tags in accordance with said inputted reaction signals;
instructions for reading transmitter station codes included in said inputted reaction signals and instructions for registering data representing positions of tags in accordance with transmitter station codes included in said inputted reaction signals;
instructions for comparing inputted reaction signals with a predetermined warning condition, instructions for generating a warning signal if the inputted reaction signal matches the predetermined warning condition, and instructions for causing said comparing and generating instructions to be carried out in real-time;
instructions for registering data representing positions of personal tags in accordance with inputted reaction signals including the transmitter station code included in the received activation signal that caused the reaction signal to be transmitted;
instructions for combining said data representing positions of personal tags with data representing positions of tags that have been received by the receiver station in a common period of time; and
instructions causing said warning signal not to be generated or to be generated in modified form in response to data representing a combination of a reaction signal matching a warning condition and a reaction signal including a predetermined personal tag code and including the same transmitter station code as the transmitter station code included in the reaction code matching the warning condition.
Further objects, features, effects and details of the invention are set forth in the description of exemplary embodiments of the invention.